Sieve of Eratosthenes benchmarks for the Z8 FORTH microcontroller

6. IMPROVING THE EFFICIENCY OF THE INNER LOOP
To take advantage of an alternative method of marking the multiples, notice that the
BEGlN..WHlLE..LOOP consists of marking the last row of an N by SIZE/N matrix with
zeros except for the cell in the first column. In the case of N=3, the result of the
inner calculation is:
A1 A4 A? A10 ... ASIZE/3-2
A2 A5 A8 All ... ASIZE/J-l
1 0 0 0 ... 0
Once the relation of the multiple-marking process to matrix operations is recognized, a
more efficient method of initializing the FLAGS array is possible using a FOKTIl word
(FILL-ROW) to initialize a row of a FLAGS array in matrix format.6 After using
FILL-ROW, the program must reset the initial element of the row back to 1. The four
arguments for the FILL-ROW word are similar to those for FILL, except that extra
parameters for the row index and column length are inserted after the array-name
argument. The stack situation when calling FILL-ROW must be programmed to be:
Array name, Rou index, Colm length, Array size, Initialization value
Modifying the FORTH program to use the word FILL-ROW results in the program shown
at the top of the next page:
‘An implementation of the word FILL-ROW for 28 FORTH is provided in Appendix B.
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